La Grande Storia degli Scacchi has William Robertson at this event. Di Felice has James Alexander Robertson. Staunton has Col. Robertson in the Illustrated London News (Nov. 9, 1867), as does Sergeant. No mention of a play-off match for 3rd prize is made by Sergeant, Gaige, Feenstra Kuiper, Reichhelm, La Grande Storia degli Scacchi or any of the primary sources, but Di Felice has a 1-1 score for a play-off between MacDonnell and de Vere. Some of the primary sources indicate that 3rd and 4th prizes were split between the two, but that would be consistent with a tied play-off or no play-off. La Stratégie (p.241) says that they split the prizes by common accord, which does not sound like a play-off was played. Renette and Zavatarelli explicitly say they split the prizes without a play-off. Without clearer evidence for a play-off, I will not include this result. La Grande Storia degli Scacchi has 3-12 Sep.; Di Felice has 3-14 Sep. Renette and Zavatarelli say the first round started 4 Sep.